Elk City aquifer report
Water use and general info

The Elk City Aquifer underlies parts of Beckham, Custer, Roger Mills,
and Washita Counties in western Oklahoma and covers 519 square miles.
The mean annual water use was 2,314 acre ft from 1967-2018,
corresponding to roughly 2.1 million gallons per day (Wagner et
al. 2021).
Water level trends
To view and download continuous water level data for the Elk City
aquifer, go to the web page below:
INSERT R SHINY APP LINK ONCE IT IS QA’d
DISCLAIMER: THIS IS ONE POSSIBLE TREND CALCULATION METHOD BUT
REQUIRES MORE COMMUNICATION/DISCUSSION BEFORE IT IS MADE PUBLIC
The general change in water level for all continuous recorders are
listed below, in ft/yr. These were calculated by taking the median water
level for each month and using the seasonal Mann-Kendall’s test to
determine the trend after filtering out seasonal influence.
|
Well
|
Trend Slope (ft/year)
|
p value
|
|
20880
|
0.611
|
4e-07
|
Over the last 10 years, there has been a statistically significant
increase in water level in continuous water level recorder site 20880,
with an increase of approximately 0.6 ft/yr
Find or download well water levels
EPA-regulated contaminants
Primary Maximum Contaminant Levels
The EPA has established National Primary Drinking Water Regulations,
called Maximum Contaminant Levels (MCL) to protect the public against
consumption of drinking water contaminants that present a risk to
human health. These are shown along with the aquifer
statistics in Table 1 below:
Table 1: Aquifer statistics and EPA Primary MCL
values. Green result values with down arrows indicate that aquifer
median concentrations are below the MCL. Red values with up arrows
indicate that aquifer median results are above the MCL. A “<” symbol
indicates the result value is below the laboratory reporting limit.
Median* = estimated aquifer-wide median using bootstrapping, a robust
statistical method; μg/L = micrograms per liter (1 g/L = 1,000,000
μg/L); mg/L= milligrams per liter (1 g/L = 1,000 mg/L).

No median aquifer concentrations of EPA primary contaminants exceed
their MCL’s, but some individual wells meet or exceed MCL’s for arsenic,
cadmium, and nitrate/nitrite.
Secondary Maximum Contaminant Levels
The EPA has established non-mandatory National Secondary Drinking
Water Regulations, called Secondary Maximum Contaminant Levels (SMCL),
to assist public water systems in managing their drinking water for
aesthetic considerations such as taste, color, and
odor. These contaminants are NOT considered to present
a risk to human health at the SMCL. The SMCLs and aquifer statistics are
in Table 2 below:
Table 2: Analytical results and EPA Secondary SMCL
values. Green result values with down arrows indicate results are below
the SMCL. Red values with up arrows indicate results are above the SMCL.
A “<” symbol indicates the result value is below the laboratory
reporting limit.

No median aquifer concentrations of EPA secondary contaminants exceed
their MCL’s, but some individual wells meet or exceed MCL’s for total
dissolved solids (TDS) and mananese.
EPA Health Advisories
The EPA has issued additional health advisories for
some parameters in drinking water. These health advisory values and the
aquifer statistics are shown in Table 3 below:
Table 3: Analytical results and EPA Health Advisory
values. Green result values with down arrows indicate median
concentrations below the Health Advisory. Red values with up arrows
indicate median concentrations that are above the Health Advisory. A
“<” symbol indicates the result value is below the laboratory
reporting limit.

Median sodium concentrations for the Elk City Aquifer exceed EPA
health advisory concentrations. No other contaminants meet or exceed
health advisory concentrations.
General Chemistry
Most samples in both 2013 and 2019 indicate a calcium magnesium
bicarbonate water type, with almost equal amounts of calcium and
magnesium.
Find or download geochemical data
Click the link below to download all water chemistry data for the Elk
City aquifer.
Download aquifer chem data
You can also select results from the most recent sample for each
individual site with the table below: